Molded article of liquid crystal polymer

ABSTRACT

Complex-shaped articles formed by gas-pressure-molding composite preforms of liquid crystal polymer and porous polytetrafluoroethylene material are described. Processes for making the composite material preforms and parisons needed for gas-pressure-molding methods, such as vacuum-molding and blow-molding, are also described.

FIELD OF THE INVENTION

The invention relates to complex-shaped articles comprising a liquidcrystal polymer or liquid crystal polymer alloy, more specifically, tosuch articles made by methods such as blow-molding, vacuum-forming, orthe like.

BACKGROUND OF THE INVENTION

Liquid crystal polymers are a family of materials that exhibit a highlyordered structure in the melt, solution, and solid states. They can bebroadly classified into two types; lyotropic, having liquid crystalproperties in the solution state, and thermotropic, having liquidcrystal properities in the melted state.

Further discussion of liquid crystal polymers hereinbelow refers only tothermotropic liquid crystal polymers, i.e., those liquid crystalpolymers and liquid crystal polymer alloys which are processed in themelted state. Also, liquid crystal polymer, as used herein, is meant toinclude polymer alloys having a liquid crystal polymer component as wellas liquid crystal polymers alone. For convenience, the term "liquidcrystal polymer" is used herein to include material of both kinds.

Most liquid crystal polymers exhibit excellent physical properties suchas high strength, good heat resistance, low coefficient of thermalexpansion, good electrical insulation characteristics, low moistureabsorption, and are good barriers to gas flow. Such properties make themuseful in a broad range of applications in the form of fibers, injectionmolded articles, and, in sheet form, as electronic materials for printedcircuit boards, packaging, and the like.

Many of the physical properties of liquid crystal polymers are verysensitive to the direction of orientation of the liquid crystal regionsin the polymer. The ordered structure of the liquid crystal polymer iseasily oriented by shear forces occurring during processing and highlyaligned liquid crystal chains can be developed that are retained in thesolid state, and result in highly anisotropic properties. This can behighly desirable for certain products, for example, in filaments,fibers, yarns, and the like. Anisotropic properties are often notdesirable, however, in products having planar forms, such as tape,films, sheet, and the like.

A number of methods are used to produce liquid crystal polymer materialsin planar forms that have more balanced, less anisotropic properties.These include the use of multilayer flat extrusion dies which arefashioned such that they extrude overlapping layers at intersectingangles, use of static mixer-agitators at the die inlets, and the like.More recently, dies having rotating or counter-rotating surfaces havebecome known in the art and successfully used. These extrusiontechniques, used separately or in combination with other methods knownin the art, such as film blowing, can produce liquid crystal polymerfilm and sheet that are multiaxially oriented, that is, oriented in morethan one direction, and have more balanced physical properties.

Also known in the art are methods to produce planar forms in which aliquid crystal polymer film is laminated to a porous polymeric supportmembrane to form a composite sheet, and the composite sheet thenstretched in one or more directions to multiaxially orient the liquidcrystal polymer. Such methods are disclosed in European PatentApplication No. EP 0 612 610 and U.S. Pat. No. 5,534,209 (to Moriya).

Unlike most other thermoplastic polymer resins, thermotropic liquidcrystal polymers form high-viscosity melts having thixotropiccharacteristics. The melt viscosity of such materials, and theorientation of the liquid crystal polymer domains, are substantiallyaltered in response to shear forces applied to the melted material. Asnoted above, these attributes can be very useful and are taken advantageof in the manufacture of articles having anisotropic properties and, toa large degree, can be controlled in the manufacture of articles havingplanar forms such as sheet, film, or other flat-shaped objects in whichmore balanced properties may be desired. However, due to theseattributes, it is extremely difficult to form hollow or othercomplex-shaped articles of liquid crystal polymers using moldingtechniques commonly used with many other thermoplastic polymer resins,especially techniques such as blow-molding or vacuum-forming, in which agas pressure differential across a polymer preform is used to force thepreform against the molding surfaces. Consequently, molded articles ofliquid crystal polymers formed by such techniques have yet to bedeveloped.

It is a purpose of this invention to provide complex-shaped articlescomprising a liquid crystal polymer, and further to provide methods bywhich such articles can be made by gas-pressure-differential moldingtechniques.

SUMMARY OF THE INVENTION

The invention provides thin-walled articles having complex non-planarshapes, formed by a gas-pressure-molding method, made of a compositematerial comprising a liquid crystal polymer and porouspolytetrafluoroethylene material. By thin-walled articles is meantarticles in which the thickness of the composite material forming thearticle is much less than the dimensions or spaces defined by thearticle. For example, food or pharmaceutical containers, automotive gastanks, bottles or other vessels, and the like.

Gas-pressure-molding (or gas-pressure-forming) is used herein todescribe methods in which air or other gas is applied or removed tocreate positive pressure or negative pressure at one side of a moldingpreform or parison, and thereby is used to assist in shaping and formingan article. Gas-pressure-molding thus includes methods moreconventionally known as vacuum-forming or vacuum-molding, plug-assistvacuum-forming, air-pressure-forming, blow-molding, etc., andcombinations thereof. It is to be understood that in the course ofgas-pressure-molding the gas pressure may be varied on one or both sidesof the parison or preform, either simultaneously or sequentially.

The composite material forming the wall(s) or sides of the article hasat least three distinct regions through its thickness; an outermostregion of porous polytetrafluoroethylene material only, an inner regionof liquid crystal polymer only, and an intermediate region between theother two regions which contains both liquid crystal polymer andpolytetrafluoroethylene materials; the intermediate region being formedby impregnation of a portion of the liquid crystal polymer forming theinner region into at least a portion of the pores of the inward-facingsurface of the porous polytetrafluoroethylene material. Anotherembodiment of the invention is a molded article in which the compositematerial forming the article has more than three disinct regions. Thisembodiment consists of a region of liquid crystal polymer onlysandwiched between two regions of porous polytetrafluoroethylenematerial only between which intermediate regions containing both liquidcrystal polymer and polytetrafluoroethylene material have been formed asdescribed above.

A further embodiment of the invention is a parison for blow-molding acomplex-shaped article. The parison comprises a tube of liquid crystalpolymer material having at least one layer of porouspolytetrafluoroethylene material fixed to its outer surface. The parisoncan also have one or more layers of porous polytetrafluoroethylenematerial fixed to its inner surface.

Yet a further embodiment of the invention is a method forgas-pressure-molding a complex-shaped article. The method includesforming a composite preform sheet having at least five distinct regionsthrough its thickness; two outermost regions (i), each outermost regionformed of a porous polytetrafluoroethylene material only, an innerregion (iii) of liquid crystal polymer only, and two intermediateregions (ii) containing both liquid crystal polymer andpolytetrafluoroethylene, each of the intermediate regions (ii) locatedbetween an outermost region (i) and the inner region (iii). Thecomposite preform thus formed is disposed over a mold, so as to form aclosed cavity, and heated to a temperature greater than the melttemperature of the liquid crystal polymer. A gas pressure-differentialfrom one side of the preform to the other is created so as to cause thepreform to deform and conform to the molding surfaces of the mold,thereby forming a shaped article. The article is then cooled and removedfrom the mold.

Another embodiment of the invention is another method forgas-pressure-molding a complex shaped article. The method includesdisposing a parison described hereinabove in a shaped mold forblow-molding. The interior of the parison is pressurized with a heatedgas so as to heat the parison to a temperature greater than the melttemperature of the liquid crystal polymer thereby causing the parison toexpand and conform to the molding surfaces of the mold. The shapedarticle thus formed is cooled and removed from the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of a complex-shaped moldedarticle of the invention having three distinct regions through thethickness of the composite material.

FIG. 2 is a cross-sectional view of a portion of a complex-shaped moldedarticle of the invention, or a molding preform, having five distinctregions through the thickness of the composite material.

FIGS. 3, (a) through (f), are cross-sectional views of an apparatusrepresentative of various steps in molding an article by agas-pressure-molding method.

DETAILED DESCRIPTION OF THE INVENTION

As noted earlier, molding non-planar complex shapes of a thermotropicliquid crystal polymer by methods such as blow-molding or vacuum-formingis extremely difficult or impractical due to the melt properties of theliquid crystal polymer. In particular, due to the ease with which shearforces applied during molding alter the melt viscosity and orientationof the material, it is difficult to control the crystalline orientationand thickness of the liquid crystal polymer during the molding steps sothat complex-shaped articles having acceptable dimensional and physicalproperties can be produced.

The inventor has discovered that, by combining the liquid crystalpolymer with a porous material to make a composite material, acceptablearticles can be prepared by such gas-pressure-molding methods. Theporous material provides support to the liquid crystal polymer duringprocessing steps in the preparation of molding preforms or parisons, andfurther during the gas-pressure-molding steps used to form the liquidcrystal polymer article. The porous material, preferably afluoropolymer, and more preferably polytetrafluoroethylene, is alsouseful in facilitating release of a molded article from moldingsurfaces. The porous material can be kept as part of the finishedarticle, or removed, as desired.

FIG. 1 is a cross-sectional view depicting a portion of a molded articleof the invention in which the composite material forming the moldedarticle has three distinct regions through its thickness; an outerregion 1 of porous polytetrafluoroethylene material only, an innerregion 3 of liquid crystal polymer only, and an intermediate region 2containing both liquid crystal polymer and polytetrafluoroethylenematerial.

FIG. 2 is a cross-sectional view depicting a portion of a molded articleof the invention in which the composite material forming the moldedarticle has five distinct regions through its thickness; outer regions 1of porous polytetrafluoroethylene material only, an inner region 3 ofliquid crystal polymer only, and intermediate regions 2 containing bothliquid crystal polymer and polytetrafluoroethylene material.

Many thermotropic liquid crystal polymers and liquid crystal polymeralloys are known in the art, are commercially available, and can be usedin the composite material of the invention. Preferably, the liquidcrystal polymer has a melt temperature of about 250° C. or higher, morepreferably 280° C. or higher. Acceptable liquid crystal polymer melttemperatures are limited only by the properties of thepolytetrafluoroethylene component, or other components, in the compositematerial and can be as high as 380° C. or more. Examples of suitableliquid crystal polymers are aromatic polyesters that exhibit liquidcrystal properties when melted and that are synthesized from aromaticdiols, aromatic carboxylic acids, hydroxycarboxylic acids, and the like.The following three types of polymers are typical examples: The firsttype (Formula 1 below) consisting of parahydroxybenzoic acid (PHB) andterephthalic acid; the second type (Formula 2 below) consisting of PHBand 2,6-hydroxynaphthoic acid; and the third type (Formula 3 below)consisting of PHB, terephthalic acid, and ethylene glycol. ##STR1##

Also, in the present invention, a polymer alloy having a liquid crystalpolymer component can be used. In such cases the polymer which is mixedwith or chemically bonded to a liquid crystal polymer can be selectedfrom the group consisting of, but not limited to, polyetheretherketone,polyphenylenesulfide, polyether sulfones, polyimides, polyetherimides,polyamides, polyamide-imides, polyesters, and polyarylates. The liquidcrystal polymers and alloying polymers can be mixed in a weight ratio of10:90 to 90:10, preferably in the range of 30:70 to 70:30. The alloyingpolymer should have a melt temperature of 200° C. or more, preferably250° C. or more, and more preferably in the range 280° to 380° C.

The liquid crystal polymers and liquid crystal polymer alloys describedhereinabove are meant for illustration and not for limitation of theinvention. It is recognized by the inventor that many other liquidcrystal polymers and liquid crystal polymer alloys suitable for use inthe invention are known in the art. Likewise it is recognized thatcompatibilizers, plasticizers, flame retardant agents, and otheradditives; or particulate fillers such as fibers or powders of glass,alumina, silica, titania, zirconia, and the like, may be included withthe liquid crystal polymers.

The material forming the porous outer region 1 should have high chemicalresistance and high electrical insulating properties, and also, highheat resistance so as to be processible at the melt temperature of aliquid crystal polymer with which it is in contact. Fluoropolymers suchas polytetrafluoroethylene, tetrafluoroethylene/hexafluoropropylenecopolymer, tetrafluoroethylene/(perfluoroalkyl) vinyl ether copolymer,polyvinyl fluoride, polyvinylidene fluoride,ethylene/tetrafluoroethylene copolymer, polychlorotrifluoroethylene, andthe like, have such characteristics and can be used.Polytetrafluoroethylene is the preferred fluoropolymer. In addition toits well known chemical inertness, excellent dielectric properties, andhigh termperature resistance, polytetrafluoroethylene has processingcharacteristics unique among fluoropolymers. Although considered athermoplastic polymer, as are the other fluoropolymers listed above,polytetrafluoroethylene is not melt processible; does not form a liquidmelt, as do the other fluoropolymers; remains solid when heated aboveits melt temperature and, furthermore, does not begin to thermallydegrade until temperatures in excess of 400° C. are reached.

Porous polytetrafluoroethylene sheet or membrane suitable for use in theinvention can be made by processes known in the art, for example, bystretching or drawing processes, by papermaking processes, by processesin which filler materials are incorporated with the PTFE resin and aresubsequently removed to leave a porous structure, or by powder sinteringprocesses. Preferably the porous polytetrafluoroethylene film is porousexpanded polytetrafluoroethylene film having a structure ofinterconnected nodes and fibrils, as described in U.S. Pat. Nos.3,953,566 and 4,187,390 which describe the preferred material andprocesses for making them. The porous polytetrafluoroethylene membraneshould have a pore volume in the range 10 to 95 percent, preferably inthe range 50 to 90 percent; and a nominal pore size in the range 0.05 to5 micrometers, preferably in the range 0.2 to 1 micrometers.

To form a non-planar complex-shaped article by a gas-pressure-moldingmethod such as vacuum-molding, the porous polytetrafluoroethylenematerial and liquid crystal polymer are first combined to form acomposite sheet which serves as a preform for the molding step.Composite sheets useful as such preforms, and methods to make them, aredisclosed in European Patent Application No. EP 0 612 610 and U.S. Pat.No. 5,534,209 (to Moriya), incorporated herein by reference.

In addition to depicting a molded article of the invention, FIG. 2 isalso illustrative of a composite preform sheet in which the compositematerial of the preform has five distinct regions through its thickness;outer regions 1 of porous polytetrafluoroethylene material only, aninner region 3 of liquid crystal polymer only, and intermediate regions2 containing both liquid crystal polymer and polytetrafluoroethylenematerial. The regions of the preform are maintained in the samerelationship during the molding steps and the difference between thepreform sheet and the molded article is in the non-planar complex shapeof the gas-pressure-molded article.

The composite preform sheet can be made by conventional laminationmethods. For example, a liquid crystal polymer film can be interposedbetween two porous polytetrafluoroethylene membranes and adheredtogether by application of heat and pressure by heated platens, or bypassage through the nip of heated calender rolls. Typically, thetemperature of the platens or rolls are in the range 10° to 50° C.higher than the melt point of the thermotropic liquid crystal polymer.In the lamination step an amount of liquid crystal polymer, sufficientto securely bond it to the support membrane, is forced into the pores ofthe surface region of the porous support membrane and mechanicallyinterlocks with the pore structure of the porous support membrane. Thebond strength between the liquid crystal polymer and porouspolytetrafluoroethylene membrane increases with the amount of liquidcrystal polymer penetrated into the porous membrane. Greater or lesserbond strength between the materials, above that needed for preformpreparation or gas-pressure-molding, can be obtained by use of porouspolytetrafluoroethylene membranes having different pore sizes and porevolumes and/or by varying lamination temperature and pressure. Theliquid crystal polymer should penetrate the porouspolytetrafluoroethylene membrane to a depth of at least 3 percent of themembrane thickness, preferably to a depth in the range 10 to 90 percentof the membrane thickness, and most preferably to a depth of 40 to 60percent of the membrane thickness.

To prepare a preform sheet having porous polytetrafluoroethylenematerial on one side only, a sheet of nonporous release material can besubstituted in place of one of the porous polytetrafluoroethylenemembranes and lamination effected as described above, after which therelease sheet can be separated from the composite sheet. A preform sheethaving porous polytetrafluoroethylene material on one side only can alsobe prepared by superposing a liquid crystal polymer film on a porouspolytetrafluoroethylene membrane, applying heat by platen or calenderroll from the polytetrafluoroethylene side only, and superficiallymelting the liquid crystal polymer film to effect penetration of anamount of liquid crystal polymer into the porous polytetrafluoroethyleneas described above. Alternatively, the liquid crystal polymer may beapplied by direct extrusion of a film onto the surface of the porouspolytetrafluoroethylene support membrane. It is also possible to preparea composite preform sheet having porous polytetrafluoroethylene materialon one side only by removing a porous polytetrafluoroethylene membranefrom one side of a composite sheet having a porouspolytetrafluoroethylene membrane on both sides. This is facilitated whenthe membranes are bonded to the liquid crystal polymer film withdifferent bond strengths as described earlier.

The porous polytetrafluoroethylene membrane used in the compositepreform sheet can be as much as 500 micrometers thick, but is preferablyin the range 1 to 300 micrometers thick, and more preferably in therange 10 to 100 micrometers thick. The thickness of the liquid crystalpolymer film used in the composite preform sheet should be 5 micrometersor greater, preferably in the range 0.005 to 3 mm, and is determinedaccording to the product to be made from the preform. The thickness ofthe porous polytetrafluoroethylene membrane should be in the range 5 to80 percent, preferably in the range 10 to 50 percent, of the thicknessof the liquid crystal polymer film.

It is preferable that the composite preform sheet be stretched in one ormore directions in order to multiaxially orient the liquid crystalpolymer and obtain a composite preform sheet which has relativelybalanced physical properties, at least in the machine-direction andtransverse-direction; or to preferentially orient the liquid crystalpolymer in certain directions to compensate for orientation forces whichmay be imparted to the composite preform sheet in a subsequent moldingstep. Suitable stretching methods are disclosed in European PatentApplication No. EP 0 612 610 and U.S. Pat. No. 5,534,209 (to Moriya),included herein by reference.

Longitudinal direction, x-direction, and machine direction (MD) as usedherein indicate the direction of manufacture of a film or sheet;transverse direction (TD) and y- or z-direction indicate directionsnormal to the direction of manufacture.

In the stretching step the composite preform sheet is heated to atemperature at or above the melt point of the liquid crystal polymerand, preferably stretched in at least two directions. Stretching in atleast two directions may be done simultaneously or sequentially, and maybe done in one or more steps. The amount of stretch, relative tooriginal planar x-y directions, is ordinarily in the range 1 to 10:1 inthe machine (x) direction, preferably in the range 1 to 5:1; and in thetransverse (y) direction in the range 1 to 20:1, preferably in the range3 to 15:1.

Stretching may be done using conventional equipment or apparatus knownin the art. For example, multiaxial simultaneous stretching can be doneusing a radial stretching pantograph; and biaxial stretching in theplanar x-y directions can be done, simultaneously or sequentially, usingan x-y direction stretching pantograph. Also, equipment providingsequential uniaxial stretching can be used, for example, a machinehaving a section containing differential speed rolls for stretching inthe machine direction (MD), and a tenter frame machine for stretching inthe transverse direction (TD).

The composite preform sheet thus produced is useful as a preform forproducing complex-shaped articles by gas-pressure-molding such asvacuum-forming, plug-assisted vacuum-forming, and the like. In suchmethods the composite sheet preform is first positioned over a mold toform a cavity, and then sealed around the mold so that the cavity can beuniformly pressurized or evacuated. The preform is then heated to atemperature greater than the melt point of the liquid crystal polymerand a gas pressure differential created between one side of the preformand the other side. The gas pressure differential causes the preform todeform and conform to the surfaces of the mold. It is believed that thepresence of the porous polytetrafluoroethylene membrane in the compositepreform sheet aids in uniformly distributing the deformation forces andinhibits or prevents localized or nonuniform shear forces from beingapplied to the liquid crystal polymer component; and thereby preventsblowouts or localized thinning of the liquid crystal polymer component.

With reference to FIG. 3 a method for gas-pressure-molding is describedhereinbelow. FIG. 3(a) depicts a plug-assist vacuum-molding apparatusconsisting of a male plug 10, preform clamps 11, 12, and female mold 20,in axial alignment. The female mold 20 has a port 21 for introduction orremoval of a gas. In FIG. 3(b) a preform 5 has been inserted in theclamps and the clamps closed. Heater assembly 14 has been positioned toheat the preform to the molding temperature. Referring to FIG. 3(c),when the molding temperature has been reached, the heater is removed andthe clamped preform 5 (represented by the dotted line) lowered acrossthe opening of the female mold 20 and sealed around the opening toprevent gas leakage. Heated gas is introduced into the female mold 20through the port 21 and the cavity 17 formed by the preform and femalemold is pressurized. The preform 5 (now represented by the solid line)is forced by the heated gas to uniformly expand outward from the mold,much as a balloon inflates, a predetermined amount. The heated gas isthen released back through the port and, as the gas pressure drops, themale plug 10 is lowered against the expanded preform 5 and proceeds toform it and push it into the female mold as the gas pressure in thespace between the preform and the female mold drops. The gas pressure inthe cavity is further reduced by evacuation of residual gases outwardthrough the port to draw the preform 5 against the wall of the femalemold. The male plug 10 ends its travel in the female mold 20, as shownin FIG. 3(d), to complete the shaping of the article. In FIG. 3(e) themale plug 10 has been removed, the molded article 15 and female mold 20cooled by any acceptable means, for example, by fans 30 blowing air onthem. In FIG. 3(f), the molded article 15 has been removed from thefemale mold 20 and clamps 11, 12, holding the molded article opened.

The method described above is useful in illustrating the different waysin which a differential gas pressure can be applied to either or bothsides of a preform to obtain a complex-shaped article bygas-pressure-molding. In this case a positive gas pressure and,sequentially, a negative gas pressure (vacuum) are applied to the sameside of a composite preform sheet thereby creating a first gas pressuredifferential across the preform by which the preform is deformed in onedirection and, sequentially, creating a second pressure differentialacross the preform by which the preform is forced in the oppositedirection. It is readily apparent that a differential gas pressure forexerting molding and shaping forces on a preform can be used singly, orin sequential or simultaneous combination. For example, a positivepressure can be applied to one side of a preform simultaneous withapplication of a negative pressure (vacuum) to the other side.

To form a non-planar complex-shaped article by a gas-pressure-moldingsuch as blow-molding, the porous polytetrafluoroethylene material andliquid crystal polymer are first combined to form a parison, i.e., ahollow tubular preform to be formed into a hollow object byblow-molding. The parison comprises a tube of liquid crystal polymermaterial having at least one layer of porous polytetrafluoroethylenematerial fixed to its outer surface. The parison can also have one ormore layers of porous polytetrafluoroethylene material fixed to itsinner surface.

To make the parison a tube or hollow cylindrical shape of liquid crystalpolymer is first provided. The tube of liquid crystal polymer can bemade by extrusion, injection molding, extrusion blow-molding, injectionblow-molding, or by other methods known in the art. Tubes of liquidcrystal polymer made by these or other methods will generally beoriented in the longitudinal direction. In this instance, however, thisis not a problem as, in the blow-molding step, the tube is stretched orexpanded radially, in a direction generally perpendicular to thedirection of orientation making it possible to obtain a blow-moldedarticle with well balanced properties.

A porous polytetrafluoroethylene layer is fixed to at least the outersurface of the liquid crystal polymer tube. By "fixed" is meant onlythat the layer of porous polytetrafluoroethylene material be attached tothe tube sufficiently strongly to withstand further processing. As nosubsequent stretching step is needed, as in the case of the compositepreform described above, the porous polytetrafluoroethylene material canbe attached to the liquid crystal polymer tube by wrapping porous apolytetrafluoroethylene membrane or tape, having the pore size and porevolume characteristics specified earlier, on the tube sufficientlytightly to permit handling and insertion onto a blow-molding fixture.The porous polytetrafluoroethylene material can be helically orlongitudinally wrapped around the liquid crystal polymer tube, in singleor multiple layers. The porous polytetrafluoroethylene layer can also beformed on the inner or outer surfaces of the liquid crystal polymer tubeusing porous polytetrafluoroethylene tubing. In this case, it iscustomary to use porous polytetrafluoroethylene tubing having inside andoutside diameters such that a friction fit between the liquid crystalpolymer and porous polytetrafluoroethylene surfaces can be obtained. Anadhesive can also be used to attach the porous polytetrafluoroethyleneto the liquid crystal polymer tube, but is generally not needed. Theporous polytetrafluoroethylene tubing should also have the pore size andpore volume characteristics specified earlier.

The wall of the liquid crystal polymer tube comprised in the parisonshould be in the range 0.2 to 5 mm thick, preferably in the range 1 to 3mm thick. The porous polytetrafluoroethylene layer should be in therange 25 to 500 micrometers thick, preferably in the range 10 to 300micrometers thick. The porous polytetrafluoroethylene layer should bethinner than the liquid crystal polymer layer, preferably being 1/50 to1/3 as thick, more preferably 1/10 to 1/5 as thick as the liquid crystalpolymer layer.

Blow-molding a complex-shaped article using the parison described aboveis done using equipment and methods known in the art. The parison ismounted in a conventional blow-molding apparatus, heated and pressurizedinternally by heated gas to a temperature greater than the melttemperature of the liquid crystal polymer, and expanded to conform tothe shaping surfaces of the blow-molding mold. In the blow-molding stepthe liquid crystal polymer is melted and an amount of liquid crystalpolymer is forced into the pores of the surface region of the poroussupport membrane and mechanically interlocks with the pore structure ofthe porous polytetrafluoroethylene layer. The bond strength between theliquid crystal polymer and porous polytetrafluoroethylene layerincreases with the amount of liquid crystal polymer penetrated into theporous layer. Greater or lesser bond strength between the materials canbe obtained by use of porous polytetrafluoroethylene material havingdifferent pore sizes and pore volumes and/or by varying blow-moldingtemperature and pressure.

The porous polytetrafluoroethylene material comprised in the compositepreform sheet or blow-molding parison, in addition to providing neededsupport during the gas-pressure-molding steps, also serves as anexcellent mold-release material, greatly facilitates removal of themolded article from the mold and prevents contamination of the moldsurfaces by melted liquid crystal polymer. However, depending on the enduse of the article, it may be desirable to remove the porouspolytetrafluoroethylene material from one or both surfaces of the moldedarticle. Removal of the porous material from the surface of a moldedarticle can be facilitated by minimizing the bond strength between theporous polytetrafluoroethylene to be removed and the liquid crystalpolymer by the methods described above.

EXAMPLE 1 Composite Preform Sheet

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was melted in a uniaxial extruder (screwdiameter: 50 mm) and extruded through a T-die (lip length: 500 mm; lipclearance: 1 mm; die temperature 320° C.), and cooled to produce a film250 micrometers thick.

The liquid crystal polymer film was interposed between two expandedpolytetrafluoroethylene membranes (nominal pore size: 0.2 μm; porevolume: 80%; thickness: 40 μm) and laminated together by application ofheat and pressure in passage between calender rolls heated to 330° C. ata rate of 2 m/min to form a composite sheet. The composite sheet wascooled by passage between two cooling rolls (roll temperature: 150° C.;roll diameter: 50 mm).

The composite sheet was subsequently sequentially stretched biaxially anamount of 3:1; an amount 1.2:1 in the machine direction, and an amount2.5:1 in the transverse direction. Stretching temperature was 315° C.and the stretch rate was 10% per second. After stretching the compositesheet was heat treated for 10 minutes at 260° C.

The composite preform sheet thus formed was about 70 micrometers thick.Liquid crystal polymer had penetrated into each of the porouspolytetrafluoroethylene membranes to form a region about 10 micrometersthick containing both liquid crystal polymer andpolytetrafluoroethylene.

EXAMPLE 2 Composite Preform Sheet

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was extruded through a T-die at atemperature of 350° C., and cooled to produce a film 1 mm thick.

The liquid crystal polymer film was interposed between two expandedpolytetrafluoroethylene membranes (nominal pore size: 0.2 μm; porevolume: 80%; thickness: 100 μm) and laminated together by application ofheat and pressure between platens heated to 350° C. at a pressure of 20kg/cm² to form a composite sheet.

EXAMPLE 3 Plug-Assist Vacuum-Molded Article

The composite preform sheet of Example 2 was molded in the apparatusdepicted in FIG. 3. The female mold diameter was about 100 mm and themold height was about 33 mm. The walls of the male plug and female moldwere tapered about 3° and the corners of the male plug and female moldhad a radius of 2 mm.

The mold temperature was 330° C. and the composite preform sheet washeated to 350° C. before the heaters were removed, and the molding stepscompleted as described hereinabove with reference to FIG. 3. Thefininshed molded article was a cylindrical container having a wallthickness of 0.4 to 0.7 mm.

EXAMPLE 4 Blow-Molded Article

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was extrusion-blow-molded to form a tube20 cm long, 20 mm inside diameter, and having a wall 1 mm thick.

The liquid crystal polymer tube was spirally-wrapped with two layers ofexpanded polytetrafluoroethylene membrane (nominal pore size: 0.2 μm;pore volume: 80%; thickness: 50 μm) to form a composite blow-moldingparison. The membrane was wrapped sufficiently tightly to hold itself inplace and no adhesive was needed to attach it to the liquid crystalpolymer tube.

The parison was mounted in a conventional bottle-forming mold. The moldwas heated to 320° C. and air heated to 380° C. was forced into theparison for blow-molding, after which the mold was opened and the formedarticle cooled. The article formed was a bottle 22 cm long.

EXAMPLE 5 Blow-Molded Article

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was extrusion-blow-molded to form a tube10 cm long, 10 mm inside diameter, and having a wall 2 mm thick.

The liquid crystal polymer tube was spirally-wrapped with four layers ofexpanded polytetrafluoroethylene membrane (nominal pore size: 0.2 μm;pore volume: 80%; thickness: 50 μm) to form a composite blow-moldingparison. The membrane was wrapped sufficiently tightly to hold itself inplace and no adhesive was needed to attach it to the liquid crystalpolymer tube.

The parison was mounted in a conventional bottle-forming mold. The moldwas heated to 320° C. and air heated to 380° C. forced into the parisonfor blow-molding, after which the mold was opened and the formed articlecooled. The article formed was a bottle 22 cm long.

COMPARATIVE EXAMPLE 1

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was melted in a uniaxial extruder (screwdiameter: 50 mm) and extruded through a T-die (lip length: 500 mm; lipclearance: 1 mm; die temperature 320° C.), and cooled to produce a film250 micrometers thick, as described in Example 1. The liquid crystalpolymer film was not combined with porous polytetrafluoroethylenematerial.

The liquid crystal polymer film was mounted in the plug-assistvacuum-molding apparatus and molded as described in Example 3.

The molten liquid crystal polymer sheet flowed uncontrollably andadhered to the mold.

COMPARATIVE EXAMPLE 2

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was extrusion-blow-molded to form a tube20 cm long, 20 mm inside diameter, and having a wall 1 mm thick, asdescribed in Example 4. The liquid crystal polymer tube was not wrappedwith porous polytetrafluoroethylene material.

The liquid crystal polymer tube was mounted and blow-molded as describedin Example 4. One section of the liquid crystal polymer tube became verythin and a hole formed in it.

COMPARATIVE EXAMPLE 3

A thermotropic liquid crystal polymer (tradename Sumika Super E7000,made by Sumitomo Chemical Co.) was extrusion-blow-molded to form a tube10 cm long, 10 mm inside diameter, and having a wall 2 mm thick, asdescribed in Example 5. The liquid crystal polymer tube was not wrappedwith porous polytetrafluoroethylene material.

The liquid crystal polymer tube was mounted and blow-molded as describedin Example 5. One section of the liquid crystal polymer tube became verythin and a hole formed in it.

I claim:
 1. A method for gas-pressure-molding a complex-shaped articlecomprising thermotropic liquid crystal polymer material comprising thesteps of:(a) preparing a composite preform sheet, said preform sheethaving, through its thickness, at least five distinct regions; outermostregions (i) formed of a porous polytetrafluoroethylene material havingan inward-facing surface and an outward-facing surface, intermediateregions (ii) containing liquid crystal polymer material andpolytetrafluoroethylene material, and an inner region (iii) formed ofliquid crystal polymer only; said intermediate regions (ii) beingregions formed by impregnation of liquid crystal polymer material intoat least a portion of the pores of the inward-facing surface of theporous polytetrafluoroethylene material; (b) disposing said preform overa mold so as to form a closed cavity; (c) heating said preform to atemperature greater than the melt point of said liquid crystal polymer;(d) creating a differential gas pressure from one side of said preformto the other so as to cause said preform to deform and conform to themolding surfaces of said mold, thereby forming a shaped article; (e)cooling and removing said article from the mold.
 2. The method forgas-pressure-molding a complex-shaped article as recited in claim 1wherein the porous polytetrafluoroethylene material is porous expandedpolytetrafluoroethylene.
 3. The method for gas-pressure-molding acomplex-shaped article as recited in claim 1 further comprising the stepof removing the porous polytetrafluoroethylene material from at leastone side of said shaped article.
 4. The method for gas-pressure-moldinga complex-shaped article as recited in claim 2 further comprising thestep of removing the porous polytetrafluoroethylene material from atleast one side of said shaped article.